Piston



April 28, 1925.

R.v M. yBURDICK PISTON Filed.` May. 9, 1922 PATENT OFFICE.

RALPH M. BURDICK, OF LOS ANGELES, CALIFORNIA.

PISTON.

Application filed May 9, 1922. Serial No. 559,508.`

" kind of piston and cylinder mechanism; and

although the piston has been designed particularly with interna-l combustionV engines in view it will be-'understood that the invention is not at all limited to use in an internal combustion engine.

There are certain difficulties attendant the use of cast iron pistons in high speed engines; one of the primary disadvantages be- A* ing the weight of the piston which causes undue vlbratlon and necess1tates careful building of the parts in order to reduce such vibration. Cast iron pistons in order to bev made of light weight must -be 'made very thin and are liable to breakage. On the other hand pistons of aluminum or aluminum alloys, although light, have acoeiicient of expansion greater than cast iron and consequently when fitted into cast iron cylinders must be made somewhat small so that they will not bind when the average working temperature is reached. This of course, necessitates a certain looseness at lower temperatures, causing the pistons to slap and allowing excessive oil to work up into the combustion chamber, necessitating in turn `the frequent cleaning of spark plugs.

This' invention has for a general object 'the provision of a piston which has the desirable features of both the cast iron piston and the alloy piston, with none of their disadvantages. This and other objects and corresponding features of the invention will be best understood from the following detailed description of preferred forms of the invention, `reference for this purpose being had to the accompanying drawings in which I`i 1 is a longitudinal central section of one form of my improved system; Fig. 2 is a similar View of another form; and, Fig. 3 is a similar view of another form.

In making my piston I provide a piston body with a head l() and side walls 11 and with the usual lwrist-pin bearings 12, and with whatever ribbed reinforcement 13 may be rnecessary or desirable to strengthen the piston.- Although I illustrate the piston body here as having tapering side walls whlch taper from the 4head tothe skirt end of the plston but itA will be readily understood ithat the invention to which this appllcation is particularly directed is applicable to any form of piston structure proper.

VThe tapering walled structure has certain advantages in the radiation and conduction of heat from the piston; but this subject matter is to be covered by a co-pending apphcation.

In the cylindrical piston wall I set one or more cast iron bands as illustrated, in the various form of the device, at 14, 14a and 15. For instance, in Fig. 1 there is illustrated a cast iron band 14 that is put into placeafter both the piston body and the bandhave been machined by shrinking the band' onto the piston body in the well known manner. Thus in this case the band 14 is at or near the upper end of the piston, its edge being shown 1n the drawings as flush with the head surface ofthe piston. The exterior cylindrical surface of band 14 is substantially the same as or may be slightly greater' or lesser in diameter than the diameter of the piston body at that point. If larger, or of the same size it may be used as a wearing surface. This external diameter of the band 1s made with substantially the clearance used for cast iron pistons. And this band carries the piston rings 16 of any suitable number and any suitable construction.v The band is heavy enough thatthe interior expansion of the aluminum or alloy piston body will not break the band and will not cause the band to expand much more than at its normal eX- pansion rate. Of course, it is inevitable that, dueto the differential rate of expansion between the two metals, the band will be resiliently expanded Slightly over and above its normal heat expansion rate; -but the strength of the band is s o designed that the major portion, or at least a large portion, of the difference in expansion is taken up by compression of the piston body.

.When I say that the band is made of cast iron I mean merely to specify a suitable material. :Other materials of about the saine rate of expansion as cast iron .may be used, .aand which will give a good wearing engagement with the cylinder. For instance, certain types ofl steel may be used for the band; and in selecting the material 11 .for `the band it may be preferred to select one that has a co-eicient of expansion slightly less than that of cast iron; so that the ultimate expansion of the band, due to heat and due also to the larger expansion of the encircled piston body, Will cause the band to expand at the same rate, or at substantially the same rate as the cast iron cylinder. Furthermore, it will be understood that I am giving this description on the assumption that cylinders are made of cast iron. They are now commonly so made. But in a cylinder made of any other material, or containing a piston surrounding sleeve of any other material, the material of the band will be modified accordingly to make that band either of the same material or of a material having the same or substantially the same coefficient of expansion, or a slightly lesser coeflicient of expansion, as herein set forth.

In Figs. 2 and 8 I illustrate another structure which embodies the same ideas hereinabove set forth. In these cases, however, the band 14a is set at a little distance from the head surface of the piston. To form this structure the -band is rst made and machined and then pressed in the mold in which the piston body is cast, and the piston body is cast directly in the band. Whole exterior surface may then be accurately machined, the exterior surface of the band being machined concentric with the exterior surface of the piston and projecting slightly above the piston surface.

In Fig. 2 I also show a similar construction applied at the skirt end of the piston; Where a band l5 is also set in the piston body carrying a ring 17. This band 15 may be, in normal cases, a relatively narrow one carrying a single rin but it Will be understood that any of t ese bands lherein described may be made of any desired Width to carry any number of rings.

From the foregoing description and the illustrations herein given I believe my invention will be made clear. It will be understood however that these illustrations are not given for the purpose of necessarily limiting the invention to their specific details, but are given for the purpose of making the whole of my invention clear and plain to those skilled in the art. Accordingly, I do not limit the invention except as set out in the following claims.

The-

- Having described a preferred form of my invention I claim:

l. A piston for a cylinder, the piston including a piston body of a material having a coefficient of'expansio-n greater than the material of the cylinder, and a ring carrying band surrounding the piston and composed of a material having a coefficient of expansion slightly less than the coefficient of expansion o-f the cylinder material so that the expansive forces of the encircled piston body causes the band to expand substantially at the same rate as the cylinder.

2. A piston for a cylinder, the piston including a piston body of a material having a coeflicient of expansion greater than the material of the cylinder, and a cylinder bearing band surrounding the piston with its outer cylindrical surface slightly above the outer cylindrical surface of the piston and composed of 'a material having a coefiicient of expansion slightl less than the coefficient of expansion of the cylinder material so that the expansivel forces of the encircled piston body causes the band to expand substantially at the saine rate as the cylinder.

3. A piston for a cylinder, the piston including a .'piston body of aluminum-like material having a coeiiicient of expansion greater than the material of the cylinder, a cylinder bearing band encircling the piston body vvith its outer cylindrical surface projecting slightly beyond the outer cylindrical surface of thc body, piston rings carried in said band; and said band being composed of a material having a coefficient of expansion slightly less than that of thc cylinder material, so that the greater heat expansion of the encircled piston body causes the band to expand substantially at the same rate as the cylinder.

4. A piston for a cylinder, said piston including a body of suitable material, and a bandv encircling the piston and formed of a material having a coefficient of expansion slightly less than the coefficient of expansion of the cylinder material.

In Witness that I claim the foregoing I have hereunto subscribed my name this 27th day of April, 1922.

RALPH M. BURDI CK. 

